This invention relates to a gas turbine system in which a gas turbine blade and a combustor tail pipe are steam cooled.
A conventional gas turbine system is described with reference to FIG. 2. As shown in FIG. 2, a conventional steam cooled gas turbine is configured such that bleed steam from an outlet of a high pressure turbine is used as such for blade cooling, and then recovered by an intermediate pressure turbine. A tail pipe of a combustor is cooled with discharge air from a compressor.
In FIG. 2, the numeral 01 denotes a gas turbine, 02 an exhaust heat recovery boiler, 7 a high pressure turbine, 8 an intermediate pressure turbine, and 9 a low pressure turbine. In the gas turbine 01, the air is sucked into a compressor 5, and compressed there to a predetermined pressure. Then, fuel adjusted to a predetermined temperature at an inlet of a turbine 4 and air pressurized by the compressor 5 are mixed and burnt in a combustor 6.
In the turbine 4, a high temperature, high pressure combustion gas generated by the combustor 6 is expanded to produce output, which generates power in a generator 20. Exhaust gas after completion of work is supplied to the exhaust heat recovery boiler 02 through an exhaust gas duct 10.
A turbine stationary blade and a turbine moving blade of the turbine 4 are cooled with steam fed from an outlet of the high pressure turbine 7 through a blade cooling steam supply piping 11. Heated steam after cooling is recovered into an inlet of the intermediate pressure turbine 8 via a blade cooling steam recovery piping 12.
In the exhaust heat recovery boiler 02, superheated steam produced by a high pressure drum 3 is guided to the high pressure turbine 7 through a high pressure steam piping 13. Then, it is expanded in the high pressure turbine 7 to generate output.
Output steam from the high pressure turbine 7 is branched into a portion which is guided to the turbine stationary blade and moving blade of the gas turbine 01 by the blade cooling steam supply piping 11, and a portion which is guided to a reheater 24 of the exhaust heat recovery boiler 02.
Steam produced by an intermediate pressure drum 2 is mixed with outlet steam from the high pressure turbine 7. The resulting mixture is supplied to the reheater 24, where it is heated. The heated mixture is mixed with the blade cooling steam guided by the blade cooling steam recovery piping 12, and is then fed to the inlet of the intermediate pressure turbine 8.
In the intermediate pressure turbine 8, steam expands to obtain output. Outlet steam from the intermediate pressure turbine 8 mixes with steam, which has been produced by a low pressure boiler 1, via a low pressure steam piping 15. Then, the mixed steam is supplied to the low pressure turbine 9 to obtain output.
Then, steam is condensed by a condenser 21, and pressurized by a pressure pump 22 to a predetermined pressure. Then, the condensate is fed to the exhaust heat recovery boiler 02 through a feed water piping 23.
As stated earlier, according to the conventional steam cooled gas turbine, steam bled from the outlet of the high pressure turbine is used as blade cooling steam, while air discharged from the compressor is used as such to cool the tail pipe of the combustor. Thus, temperature control for cooling steam has been difficult.
Furthermore, the high temperature part of the gas turbine undergoes creep deformation, unless the metal temperature is made lower than a certain temperature. Thus, the supply temperature of cooling steam must be set to be below a certain limit. Under partial load, in particular, the cooling steam supply temperature tends to become higher than under rated load. Utmost care must be exercised about this respect.